This invention relates to equipment for the manufacture of glass containers and, more particularly, to the equipment associated with the formation of the parison in the blank mold of an I.S. (individual section) machine.
During the initial stage of the formation of a glass container on an I.S. machine, a gob of molten glass is delivered to a blank mold. The gob is settled into the blank mold and a plunger is pressed into the center of the gob to form a hollow parison. An elongate plunger is pressed a substantial distance into the gob in the well-known press-and-blow process. In the well-known blow-and-blow process, a shorter plunger is pressed into the gob to form a pocket and is then withdrawn. Air is then forced into the pocket to form the hollow parison. In each process, the hollow parison is transferred to a final mold and blown into the final shape.
In either process, the press-and-blow process or the blow-and-blow-process, the plungers must be secured to a reciprocating piston. The plungers must be secured in a manner to align them with the axis of the piston, to be held so as not to wobble and to be easily connected and disconnected to and from the piston. Since the I.S. machines are designed to make many different bottle shapes and sizes, it is necessary to be able to remove and replace the plungers at the time the blank molds are changed to make a different style bottle.
Over the years, a number of plunger assemblies for securing the plungers to the reciprocating pistons have been considered. Perhaps the earliest plunger assembly is that described with reference to FIG. 1 of Davis U.S. Pat. No. 4,033,744 entitled xe2x80x9cPlunger Assembly for a Glass Forming Machine.xe2x80x9d In that assembly, a plunger head is threaded to the end of the piston and the plunger is held on the plunger head by two split rings. The plunger assembly is located within a guide cylinder to maintain axial control of the plunger and to hold the split rings in position. The replacement of the plunger requires the removal of the guide cylinder followed by removal of the rings. The replacement plunger is then rested on the plunger head, the split rings are positioned, and the guide cylinder lowered over the split rings. Holding the plunger and split rings in place while positioning and lowering the guide cylinder is not an easy task. As the guide cylinder and guide rings wear, the alignment of the plunger is compromised and the plunger wobbles and air leaks. Applicant estimates that as much as 70% of the plunger assemblies in use today are of the split-ring type.
A considerable improvement over the split ring plunger assembly is the snap-on plunger assembly, for example, as described in the Davis patent. In that plunger assembly, the base of the plunger is provided with a plurality of ears which interlock with a plurality of flanges disposed within a recessed area within the plunger-type head. The ears and flanges are engaged by translating and rotating the plunger relative to its axis. A variation of the snap-on plunger assembly has been marketed by the Maul Bros. division of Maul Technology Corporation for over twenty years. The plunger must be slid perpendicular to its axis in order to engage the plunger head. Another snap-on plunger assembly is disclosed in Kozora U.S. Pat. No. 4,636,240 entitled xe2x80x9cPlunger Assembly for Glass Container Manufacturing.xe2x80x9d
While the snap-on plunger assemblies were a considerable improvement over the split ring plunger assemblies, with wear, they still may permit wobble and air leakage.
Since most of the plungers in use were designed for use with the split-ring type plunger assemblies, there is a considerable resistance in the field to converting to a new type of plunger assembly.
It is an advantage, according to this invention, to provide an improved plunger assembly which is easily installed and uninstalled, which prevents wobble and is not subject to the wearing action that causes prior art plunger assemblies to wobble, and which can be used with easily retrofitted plungers designed for use in prior art plunger assemblies.
It is yet a further advantage that the plunger assembly provides an air and vacuum-tight seal between the plunger and the adapter fixed to the driving piston.
Briefly, according to this invention, there is provided a plunger assembly for use in a glass bottle forming machine permitting quick exchange and self-aligning of a plunger held on a plunger driving piston. The plunger assembly comprises: a plunger having a nose end, a cylindrical base end, and an annular contact surface perpendicular to the cylindrical axis of the cylindrical base end, the base end of the plunger defined by a cylindrical exterior surface having a diameter d1 and having an annular recess therein. Preferably, the annular recess has a surface being a portion of a toroidal surface defined by the rotation of a generating circle about the cylindrical axis of the cylindrical base, the generating circle having a diameters and the annular groove being spaced from the contact surface a distance a1. The plunger assembly further comprises an adapter having a cylindrical support end and a base end, the adapter being threaded to the driving piston at the base end thereof, the cylindrical support end of the adapter terminating in a contact surface perpendicular to the cylindrical axis of the adapter for receiving the contact surface of the plunger. A coaxial central bore is provided in the support end of the adapter defined by an internal cylindrical surface having a diameter d3 just sufficiently larger than d1 enabling receipt of the base end of the plunger. The support end of the adapter has an exterior cylindrical surface and an annular groove in the exterior cylindrical surface of the adapter. A plurality of stepped radial bores extend from the central bore into the annular groove. The axes of the radial bores are spaced a distance a2 from the contact surface. The distance a2 is substantially equal to distance a1. One in each of a plurality of retaining balls radial bore have a diameter d4 substantially equal to, the diameter of the generating circle. A split ring is sized to fit in the annular groove in the exterior cylindrical surface of the adapter. The split ring has an internal diameter such that when the internal diameter bears upon the retaining balls, the retaining balls may be seated in the annular recess in the cylindrical base of the plunger.
An annular retaining spring biases the split ring and retaining balls in the annular groove in the cylindrical base of the plunger such that the plunger can be snapped into the adapter and held in place during bottle making.